Remove Android from apm agents index (#2450)

I cannot see the android sub page.. I guess it was removed and replaced
with
https://www.elastic.co/docs/reference/opentelemetry/edot-sdks/android

Author: reakaleek

reference/apm-agents/index.md

@@ -4,7 +4,6 @@
 
 This section contains reference information for APM Agents features, including:
 
-* Android
 * .NET
 * Go
 * Java
@@ -13,4 +12,4 @@ This section contains reference information for APM Agents features, including:
 * Python
 * Ruby
 * RUM JavaScript
-* iOS
+* iOS